Preheat the oven to 350°F (175°C). In a medium bowl, combine the graham cracker crumbs, sugar, and melted butter. Mix thoroughly until the crumbs are evenly moistened. Press the mixture firmly into the bottom of an ungreased 13x9-inch baking dish. Set aside.

In a large mixing bowl, beat the softened cream cheese and sugar until smooth and creamy. Add the eggs, one at a time, mixing on low speed until just combined. Pour the mixture over the prepared crust and spread evenly. Bake for 25–30 minutes, or until the center is almost set. Remove from the oven and allow it to cool.

In a small bowl, sprinkle the gelatin over the cold water and let it stand for 1 minute. Meanwhile, in a large saucepan, combine the pumpkin pie filling and evaporated milk. Heat over medium heat, stirring occasionally, until the mixture comes to a gentle boil. Stir in the gelatin mixture until fully dissolved.

In a separate bowl, whisk the eggs lightly. Gradually add a small amount of the hot pumpkin mixture to the eggs, whisking constantly, to temper them. Slowly pour the egg mixture back into the saucepan, whisking continuously. Cook over low heat, stirring frequently, until the mixture thickens enough to coat the back of a spoon. Remove from heat and allow it to cool for about 10 minutes.

Spread the cooled pumpkin filling evenly over the cream cheese layer. Smooth the top with a spatula to ensure an even layer.

Gently spread the thawed whipped topping over the pumpkin layer. For an optional decorative touch, sprinkle cinnamon or nutmeg over the top.

Cover the dish with plastic wrap or foil and refrigerate overnight to allow the flavors to meld and the layers to set. When ready to serve, slice into squares and garnish with additional whipped topping or a sprinkle of cinnamon, if desired.